Conventionally, there is a multi-air conditioner for buildings for which an air-conditioning apparatus is applied in which, by making a refrigerant circulate between an outdoor unit, which is a heat source installed outdoors, and an indoor unit installed indoors, cooling energy or heating energy is transferred to an area to be air-conditioned such as an inside of a room, and cooling operation or heating operation is adapted to be performed. As for the refrigerant employed by such the air-conditioning apparatus, for example, an HFC type refrigerant is often used. In recent years, a natural refrigerant such as carbon-dioxide (CO2) has come to be used.
There is an air-conditioning apparatus having other configurations represented by a chiller system. In such an air-conditioning apparatus, cooling energy or heating energy is generated in the heat source apparatus installed outdoors, the cooling energy or heating energy is transferred to a heat medium such as water and an antifreezing liquid through a heat exchanger installed in the indoor unit, and they are transferred to such as a fan coil unit or a panel heater, which is an indoor unit installed in the area to be air-conditioned, to perform cooling operation or heating operation. (For example, refer to Patent Literature 1.)